1. Field of the Invention
The present invention relates to a cap and tube assembly, and particularly to a fastening structure of the tube and cap assembly.
2. Description of the Prior Art
FIG. 1 shows the structure of a conventional cap 101 which is fastened to a sealed mouth 103 of a tube. The outer end of cap 101 is provided with a conical cutting edge 105. To open the sealed mouth 103, the cap 101 is removed from the tube, and the cutting edge 105 is pushed against the sealed mouth 103 until the sealed mouth 103 is broken by the cutting edge 105. In this case, a threaded portion 107 of the tube and an inner threaded portion of cap 101 are formed to perform an ordinary screwing motion and used only for fastening and unfastening the cap 101 with respect to the tube. After opening the mouth 103 by the edge 105, the edge 105 will be wet with gel like material such as chemicals contained in the tube. Such chemicals on the edge 105 will be dried and dispersed in the air to contaminate a sanitary environment.
Japanese Utility Model No. 54-134152 discloses another example of a cap. In this example, the cap is provided on its inner bottom surface with a conical cutting edge. To prevent the cutting edge from breaking a sealed mouth of the tube, an intermediate ring is arranged between the shoulder portion of tube and the cap. If it is desired to open the sealed mouth of tube, the intermediate ring is removed, and the cap is further screwed toward the tube until the cutting edge of cap breaks the sealed mouth of tube. Similar to the previous example, a threaded portion of the tube and an inner threaded portion of the cap of this example are formed to perform an ordinary screwing function and used only for fastening and unfastening the cap with respect to the tube. This example is not practical in use, because a very complicated process is required for assembling the intermediate ring in manufacturing the tube and cap assembly and for removing the intermediate ring in opening the sealed mouth of tube before use.